The present invention relates to heat exchange engineering and boiler making and, more specifically, to tubular air heaters for steam boilers, furnaces and similar installations.
In conventional tubular air heaters incorporated in high-power boilers use is made of the air and gas cross-flow circuit making it impossible to ensure effective utilisation of the available temperature gradient with a small number of passes. As a result, these types of air heaters require much metal for their fabrication and are bulky in shape.
There is known a method of increasing the temperature gradient in cross-flow air heaters by using a Z-cross-flow circuit, according to which a flow of air moving in a multipass tubular air heater from one pass to another enters into tube banks of each pass from one and the same side relative to the direction of gas flow. As a result, the simplest in construction two-pass air heater requires, all other conditions being equal, a heating surface of 20 to 40 percent smaller than any conventional two-pass cross-flow air heater.